The present invention relates to starch copolymers, prepared by the polymerization of styrene, butadiene, and/or other vinyl monomers in the presence of a colloidally-dispersed starch. Reaction products of starch with vinyl monomers are articles of commerce and have found use as binders in paper sizing and coating compositions and as components in textile sizing formulations. U.S. Pat. No. 5,003,022, the disclosure of which is hereby incorporated by reference herein discloses the preparation of such products by (1) dispersing a starch or starch derivative of specified molecular weight in water using heat and agitation, (2) adding a free radical initiator, (3) adding all monomer(s), and (4) heating to cause the decomposition of the initiator and subsequent polymerization of the monomers, While the patent states that the monomer or monomers can be added at the beginning or during the course of polymerization it exemplifies the batch polymerization system disclosed above.
Such batch polymerization systems have long been used, and they offer the advantage of simplicity. However, they are not very versatile, and are not well-suited to producing the best product uniformity, smallest particle size, or most uniform particle size distribution.
It is one object of the present invention to provide a process for starch copolymer manufacture which yields a starch copolymer latex of weight-average particle size less than 180 nm, as measured by the capillary hydrodynamic fractionation (CHDF) technique. Another object of the invention is to provide a process for the manufacture of starch copolymers which allows the safe use of highly active monomers. Still another object of the invention is to provide products prepared by such a process that are useful in sizing paper and paper products, as components in textile fiber and warp sizes, as adhesives, and as binders in surface coating compositions for architectural and industrial applications.
It is still another object of the invention to provide latex paints as industrial and architectural coatings with improved gloss and "open time." "Open time" is the period during which the paint film can be repaired or blended into an adjacent area without showing brush marks, the edge of the film, or other blemishes.
It is further desired to produce industrial and architectural coatings having improved water resistance and wet rub resistance. Other objects and advantages of the invention will become apparent from the following disclosure and illustrative examples.